The present invention relates, in particular, to protective operations when the outdoor air temperature becomes low in cooling operation in the case of an air conditioner of separation type being constituted with indoor units and outdoor units.
There is an example of the prior art about the air conditioner which is described in a Japanese Utility Model laid-open No. Hei3-77177.
In the case of a controller for an air conditioner described in the gazette, when the outdoor air temperature is higher than 20.degree. C., a fan motor of the outdoor unit is operated in H (high speed) quantity and when the outdoor air temperature is lower than 20.degree. C. the fan motor of the outdoor unit is operated in L (low speed) draft quantity to control the lowering of the pressure on the low pressure side in refrigerating circuit, and when the pressure on the low pressure side is lowered below a specified pressure, a compressor and the fan motor of the outdoor unit are stopped. Owing the constitution as described in the above, the lowering of the pressure on the low pressure side in the refrigerating circuit is prevented when the outdoor air temperature is low.
There is another example of the prior art as shown in a Japanese Utility Model laid-open No. Sho62-164531. In the case of an air conditioner described in the gazette, the outdoor air temperature is detected in a heating operation, and when the temperature becomes lower than a specified temperature, the heating operation in heat pump cycle is changed over to a heating operation by an electric heater. As described in the above, when the outdoor air temperature is low, the operation in the heat pump cycle, in other words, the operation of a compressor is stopped, that is, when the operation efficiency in the heat pump cycle is low, the operation of the compressor is stopped to prevent the unnecessary consumption of energy.
When the outdoor air temperature is specially low, there has been a trouble that the evaporation of refrigerant in an outdoor side heat exchanger is not performed sufficiently and liquid compression can be produced to break the compressor; however, as described in the above, such a breakage of the compressor is prevented by the stop of operation of compressor when the outdoor air temperature is low.
A further example of the prior art is described in a Japanese laid-open Patent Application No. Hei2-121598. In an air conditioner shown in the gazette, 3 indoor units are connected to 1 outdoor unit. A remote controller is provided to each of these indoor units, and the operation of each indoor unit is controlled by the remote controller of exclusive use.
In the conventional air conditioner, however, an abnormal stop of a compressor is operated in a lowering period of the pressure on the low pressure side in refrigerating circuit. Therefore, a low pressure switch for detecting the low pressure on the low pressure side in the refrigerating cycle is needed and also when the pressure on the low pressure side is in a normal range and the outdoor air temperature is specially lowered, the operation of the compressor is not stopped; therefore, there has been a problem, such as an occurrence of refrigerant liquid-back to the compressor.
Moreover, when an indoor side heat exchanger is acting as an evaporator, in general, condensed water (drain water) drops from the indoor side heat exchanger. In the case of the air conditioner in which the condensed water is once received with a drain pan and then the water is discharged outside the indoor unit with a pump, the condensed water is produced for a certain period of time (a period of time till the temperature of the indoor side heat exchanger reaches to the room temperature) after the stop of operation of the compressor, so that if the operation of the pump is stopped simultaneously with the stop of operation of the compressor, the condensed water may overflow from the drain pan.
In the case of the above-mentioned prior art example (a Japanese Utility Model laid-open No. Sho62-164531), when the outdoor side air temperature becomes low, the heating operation in the heat pump cycle is switched to the heating operation by the electric heater. Because of this, the capacity in the heating operation is proportional to the heat generation capacity of the electric heater.
Therefore, the electric heater of a large heat generation capacity is needed to obtain a sufficient heating capacity (For a room of about 13 m.sup.2, heat generation capacity of about 5 kW will be needed.). For general dwelling houses, however, a capacity (the maximum current capable of flowing safely through a branch circuit) is limited from the point of view of safety. For example, when the capacity is 30 A, the operating current of a circuit breaker is 20 A, so that an allowable electric heater capacity is 2 kW at a maximum; therefore, there has been a problem that the heating capacity is not sufficient when the outdoor air temperature is low.
In order to use the electric heater of the order of 5 kW, the branch circuit to be exclusively used for the electric heater has to be provided and further a large sized casing for protecting the electric heater is needed; thereby, there has been a problem that the air conditioner itself has to be a large sized one.
Further in the case of an air conditioner constituted as mentioned in the above, when a plurality of indoor units are provided, individual setting values have to be set for these indoor units and the operation controls are made to be complicated. There has been a problem that erroneous setting may occur such as the setting of different operation modes (cooling operation, heating operation, defrosting) for indoor units.
There has been a problem that the control device of the outdoor unit has to be a large sized and complicated one since the indoor units are all connected to the outdoor unit through signal lines and the outdoor unit has to communicate with all of these indoor units.